PD Dr. Hans-Gregor Hübl

Courses and Dates

Offered Bachelor’s or Master’s Theses Topics

Lateral angular momentum transport by phonons

In a solid-state system, spin angular momentum is mediated by various (quasi-)particles. Among these excitations are phonons, which can carry angular momentum over mm distances. Most importantly, exchange of spin angular momentum from these crystal lattice vibrations to excitations of the magnetic lattice is possible via magneto-elastic coupling effects. This unlocks novel means for coherent and incoherent spin transport concepts without moving charges. Your thesis will be dedicated in assessing the realization of incoherent angular momentum transfer in nanostructured systems. In your thesis you will work on an all-electrical injection and detection scheme to access incoherent angular momentum transfer. You will use state-of-the-art nanofabrication techniques using electron beam lithography and thin film deposition machines for the realization of magnon-phonon hybrid devices. You will also gain experience in cryogenic magnetotransport techniques. You will develop automated evaluation tools and work on modelling the observed phenomena.

suitable as

• Master’s Thesis Condensed Matter Physics

Supervisor: Rudolf Gross

Magnetic resonance spectroscopy in two dimensional ferromagnets

Dimensionality crucially influences the properties of materials. Two-dimensional (2d) van der Waals materials in the monolayer limit are presently heavily investigated. Within this class of materials systems with magnetic order exist, yet only limited insights have been obtained with respect to their magnetic excitation properties. A major experimental challenge is the small volume and thus low number of spins in these systems. Thus, high sensitivity techniques and large filling factors are key for successful studies of these materials. The goal of this thesis is to use planar superconducting resonators in combination with 2d van der Waals ferromagnets to study magnetic excitations at low temperatures by microwave spectroscopy. You will work on implementing the microwave-based spectroscopy of magnetic excitations in 2d systems. You will use state-of-the-art nanofabrication techniques like electron beam lithography and thin film deposition machines for the superconducting resonators. You will also gain experience in cryogenic microwave spectroscopy utilizing vector network analyzing techniques. Another important aspect will be the development of a quantitative model to illuminate the underlying physics of the magnetic excitations.

suitable as

• Master’s Thesis Quantum Science & Technology

Supervisor: Rudolf Gross

Magnon-mechanics in suspended nano-structures

Nano-mechanical strings are archetypical harmonic oscillators and can be straightforwardly integrated with other nanoscale systems. For example, the field of nano-electromechanics studies the coupling of nano-strings to microwave circuits, which resulted in the creation of mechanical quantum states and concepts for microwave to optics conversion. Here, we plan to investigate an alternative hybrid system based on ferromagnetic nanostructures integrated with nano-strings or nano-mechanical platforms. These hybrid devices aim at the efficient conversion between phonons and magnons with the potential to interact with light and are thus ideal candidates for conversion applications. We are looking for a motivated master student for a nano-mechanical master thesis in the context of magnon-phonon interaction. The goal of your project is to investigate the static and dynamic interplay between the mechanical and magnetic properties of a nano-mechanical system sharing an interface with a magnetic layer. In your thesis project, you will fabricate freely suspended nanostructures based on magnetic thin films using state-of-the-art nano-lithography and deposition techniques. Further, you will probe the mechanical response of the nano-structures using optical interferometry while exciting the magnetization dynamics of the magnetic system.

suitable as

• Master’s Thesis Quantum Science & Technology

Supervisor: Rudolf Gross

Magnon transport in laterally confined magnetic insulators

In antiferromagnetic insulators, we obtain two magnon modes with opposite spin chirality due to the two opposing magnetic sublattices. In this way, magnon transport in antiferromagnetic insulators can be considered as the magnonic equivalent of electronic spin transport in semiconductors and the properties can be mapped onto a magnonic pseudospin. At present, most experiments rely on extended epitaxial thin films of antiferromagnetic insulators. Your thesis will be dedicated to confine the lateral dimensions of the magnon transport channel. By conducting all-electrical magnon transport experiments, you will then determine the role of lateral confinement in such measurement schemes. You are interested in providing novel insights into pseudospin properties in antiferromagnetic insulators and provide a spark for theoretical descriptions. In order to answer questions regarding magnon transport in magnetic insulators, your thesis will contain aspects of the fabrication of nano-scale devices using electron beam lithography as well as ultra-sensitive low-noise electronic measurements at high magnetic fields in a cryogenic environment.

suitable as

• Master’s Thesis Condensed Matter Physics

Supervisor: Rudolf Gross

Nano-electromechanics in the non-linear regime

Circuit nano-electromechanics is a new field in the overlap region between solid-state physics and quantum optics with the aim of probing quantum mechanics in macroscopic mechanical structures. We employ superconducting circuits to address fundamental questions like the preparation of phonon number states in the vibrational mode and the conversion of quantum states between the mechanical element and the microwave domain. The initial successful experiments of the group include hybrid devices based on nano-string resonators inductively coupled to frequency tunable microwave resonators. This setting allows to explore large optomechanical single photon rates, enables intrinsic amplification schemes, and hereby allows to access a new regime of light matter coupling. The goal of your thesis is the development and fabrication of hybrid devices based on frequency tunable superconducting microwave resonators with integrated nanomechanical string-resonators as well as their spectroscopy. This includes the design and fabrication of these devices, where you will use state-of-the-art simulation and nano-fabrication techniques. The second main aspect of your thesis is their investigation using highly sensitive microwave spectroscopy techniques in a low-temperature environment.

suitable as

• Master’s Thesis Quantum Science & Technology

Supervisor: Rudolf Gross

Non-reciprocal magnonic devices

Spin waves (magnons) are the quantized excitations of the magnetic lattice in solid state systems. The field of magnonics is exploring concepts to use these magnons for information transport and processing. Of particular interest is to achieve non-reciprocity for opposite spin wave propagation directions, which can be realized in hybrid structures of a periodic artificial magnetic array on top of a magnonic waveguide. These systems would be potential candidates for compact microwave directional couplers and circulators operational at low temperatures. The goal of this thesis is to develop and optimize such nonreciprocal devices based on periodic magnetic arrays. This implementation is a first step towards compact low temperature microwave circuits relevant for superconducting quantum circuits.

You are a resourceful master student willing to contribute with your thesis towards the successful implementation of nonreciprocal microwave devices at cryogenic temperatures. You will use state-of-the-art nanofabrication techniques using electron beam lithography and thin film deposition machines to design your hybrid systems. You will also gain experience in cryogenic microwave spectroscopy utilizing vector network analyzing techniques. Utilizing a combination of numerical and analytical models, you will drive the optimization of such hybrid devices.

suitable as

• Master’s Thesis Quantum Science & Technology

Supervisor: Rudolf Gross

Optical detection of magnetization dynamics at low temperatures

Utilizing magneto-optical effects enables the investigation of excitations in magnetic systems like magnons or spin waves down to the sub-micrometer scale. In this way, one can probe spin wave propagation in micro-patterned ferromagnetic materials, which is highly relevant for spintronic applications as well the investigation of tailored quantum systems. Especially at low temperatures, novel magnetic phases exist with intriguing magnetization dynamic properties. The goal of this thesis is the optical investigation of spatially resolved magnetization dynamics in spintronic devices as well as hybrid quantum systems at cryogenic temperatures. We are searching for a highly motivated master student to start the experiments on optically detected magnetization dynamics at cryogenic temperatures. You will improve the optical setup used for the detection of magnetization dynamics to increase the sensitivity. In addition, you will work with state-of-the-art microwave equipment to drive the magnetization dynamics in spintronic devices and hybrid systems. After assessing the performance of the setup with state-of-the-art magnetic systems, you will work in the clean room facilities of our institute to carry out the microfabrication steps to define your own spintronic devices or hybrid systems.

suitable as

• Master’s Thesis Quantum Science & Technology

Supervisor: Rudolf Gross

Thin film material design for future magnonics

Spin waves (magnons) are the quantized excitations of the magnetic lattice in solid state systems. The field of magnonics is exploring concepts to use these magnons for information transport and processing. Of special interest is to obtain reliable control over the relevant properties of these magnons such as, for example, their lifetime. The goal of your thesis is to fabricate high quality magnetically ordered thin film structures and investigate their spin wave properties via microwave spectroscopy methods. You will gain experience in nanofabrication by working with state-of-the-art thin film deposition machines. Moreover, you will utilize thin film x-ray diffraction and magnetometry experiments to characterize the materials. You will utilize microwave spectroscopy techniques to extract the spin wave properties.

suitable as

• Bachelor’s Thesis Physics

Supervisor: Rudolf Gross